Look at the table below that compares AC Nielsen’s vote share and seat predictions over two successive months in 2014:

The survey estimates that the vote share of the Indian National Congress (INC) and its allies rose by a percentage point between January 2014 and February 2014, but that its Lok Sabha tally fell nine seats to 92. The vote share of the Bharatiya Janata Party (BJP) and its allies stayed about the same while their count rose ten seats to 236. Other parties’ vote share fell by about a percentage point but their projected seats fell only marginally (by a single seat) to 215.

It’s hard to say why this occurred in the absence of more details from AC Nielsen but what is clear is that the seats projection is being driven not by the vote share expectation but by other, unknown, assumptions about the distribution of those votes. These seat share projections create the illusion of momentum in favour of the BJP alliance when in fact the vote share estimates in effect show no change from the previous month.